Re: linux-next: build failure after merge of the tip tree

[Boqun Feng]

On Tue, Oct 21, 2025 at 10:18:58PM -0400, Boqun Feng wrote:
> On Wed, Oct 22, 2025 at 11:46:44AM +1100, Stephen Rothwell wrote:
> > Hi all,
> > 
> 
> Hi Stephen,
> 
> Thanks for reporting this.
> 
> Cc Mathhew and Danilo,
> 

(now really Cc them...)

Regards,
Boqun

> > After merging the tip tree, today's linux-next build (x86_64 allmodconfig)
> > failed like this:
> > 
> > error[E0594]: cannot assign to data in dereference of `lock::Guard<'_, T, MutexBackend>`
> >   --> rust/kernel/debugfs/traits.rs:64:9
> >    |
> > 64 |         *self.lock() = val;
> >    |         ^^^^^^^^^^^^ cannot assign
> >    |
> >    = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `lock::Guard<'_, T, MutexBackend>`
> > 
> 
> Could we make the `impl Reader` for `Mutex<T>` to bound where `T:
> Unpin`? Since `Mutex<T>` is structurally pinning `T`, you cannot use
> `*self.lock()` to overwrite `T` directly. And that'll fix this.
> 
> Thanks!
> 
> Regards,
> Boqun
> 
> > error: aborting due to 1 previous error
> > 
> > For more information about this error, try `rustc --explain E0594`.
> > 
> > Caused by commit
> > 
> >   da123f0ee40f ("rust: lock: guard: Add T: Unpin bound to DerefMut")
> > 
> > I have used the tip tree from next-20251021 for today.
> > 
> > -- 
> > Cheers,
> > Stephen Rothwell
> 
>